The non-local theory solution to two collinear limited-permeable mode-1 cracks in a piezoelectric/piezomagnetic medium was investigated by using the generalized Almansi＇s theorem and the Schmidt method in the present paper. The problem was for- mulated through Fourier transformation into two pairs of dual integral equations, in which the unknown variables are the dis- placement jumps across the crack surfaces. For solving the dual integral equations, the displacement jumps across the crack surfaces were directly expanded as a series of Jacobi polynomials. Numerical examples were provided to show the effects of the crack length, the distance between the two collinear cracks, the lattice parameter, the electric permittivity and the magnetic permeability of the air inside the crack on the stress fields, the electric displacement fields and the magnetic flux fields near the crack tips in a piezoeleetric/piezomaguetic medium. Different from the classical solutions, the present solution exhibits no stress, electric displacement and magnetic flux singularities at the crack tips in a piezoelectric/piezomagnetic medium.
An attempt has been made here to evaluate the effect of thermal exposure on the mechanical behavior and failure mechanisms of carbon fiber composite sandwich panel with pyramidal truss core under axial compression. Analytical formulae for the collapse strength of composite sandwich panel after thermal exposure were derived. Axial compression tests of composite laminates and sandwich panels after thermal exposure were conducted at room temperature to assess the degradation caused by the thermal exposure. Experimental results showed that the failure of sandwich panel are not only temperature dependent, but are time dependent as well. The decrease in residual compressive strength is mainly attributed to the degradation of the matrix and the degradation of fiber-matrix interface, as well as the formation of cracks and pores when specimens are exposed to high temperature. The measured failure loads obtained in the experiments showed reasonable agreement with the analytical predictions.
The solution of a 3-D rectangular permeable crack in a piezoelectric/piezomagnetic composite material was investigated by using the generalized Almansi＇s theorem and the Schmidt method.The problem was formulated through Fourier transform into three pairs of dual integral equations,in which the unknown variables are the displacement jumps across the crack surfaces.To solve the dual integral equations,the displacement jumps across the crack surfaces were directly expanded as a series of Jacobi polynomials.Finally,the relations between the electric filed,the magnetic flux field and the stress field near the crack edges were obtained and the effects of the shape of the rectangular crack on the stress,the electric displacement and magnetic flux intensity factors in a piezoelectric/piezomagnetic composite material were analyzed.
The Schmidt method is adopted to investigate the fracture problem of multiple parallel symmetric and permeable finite length mode-III cracks in a functionally graded piezoelectric/piezomagnetic material plane. This problem is formulated into dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. In order to obtain the dual integral equations, the displacement jumps across the crack surfaces are directly expanded as a series of Jacobi polynomials. The results show that the stress, the electric displacement, and the magnetic flux intensity factors of cracks depend on the crack length, the functionally graded parameter, and the distance among the multiple parallel cracks. The crack shielding effect is also obviously presented in a functionally graded piezoelectric/piezomagnetic material plane with mul- tiple parallel symmetric mode-III cracks.
A series of compression tests were conducted to investigate the mechanical properties and failure mechanisms of carbon fiber composite sandwich panels using pyramidal truss cores subjected to temperatures ranging from 100℃ to 350℃.The compressive strength and stiffness of sandwich panels decreased as temperature increased.Cryogenic temperatures caused an increase in strength and stiffness,while elevated temperatures resulted in a reduction of strength and stiffness.The effect of temperature on the failure mode of the sandwich panel was revealed as well.The interface between the fiber and matrix was examined by a scanning electron microscope(SEM) in order to study the effect of temperature on strengthening the mechanism and good bonding conditions within the fiber-matrix interface was observed at cryogenic temperatures.The comparison of the predicted and experimental data indicated that the stiffness and strength of the composite sandwich panels for temperature variation was consistent.
